Cryopumps are typically used in equipment for the manufacture of integrated circuits and other electronic components, as well as for the deposition of thin films in a variety of consumer and industrial products. The cryopumps are used to create a vacuum by freezing or pumping out gases in a work environment. Refrigerators employed by the cryopumps for pumping out gases may be open or closed-cycle cryogenic refrigerators. The most common refrigerator used is a two-stage cold finger, closed-cycle refrigerator.
Typically, the cold end of the second stage, which is the coldest stage of the two-stage refrigerator, is connected to a primary pumping surface. The primary pumping surface operates in a temperature range of 4.degree. to 25.degree. K. The first stage of the two-stage refrigerator is connected to a radiation shield which surrounds the primary pumping surface. The spacing between the primary pumping surface and the radiation shield must be sufficient to permit unobstructed flow of low-boiling temperature gases from a vacuum chamber created by the shield to the primary pumping surface. The radiation shield typically operates in a range of 70.degree. to 140.degree. K. Separating the evacuation chamber and the radiation shield is a frontal array, which also serves as a radiation shield for the primary pumping surface. The frontal array is typically cooled to 110.degree. K.-130.degree. K. By thermally coupling it to the radiation schield.
In operation, high boiling point gases, such as water vapor, are condensed on the frontal array. Lower boiling point gases pass through that array and into a volume within the radiation shielding, where they condense on the primary pumping surface. An adsorbent, such as charcoal, is typically placed adjacent to the primary pumping surface and is operated at a temperature of that surface to adsorb gases which have very low boiling point temperatures and are not condensed on the primary surface.
Multiple stage refrigerators have used temperature measuring and control devices on the first and second stages to prevent crossover hangup during cooling and for full or partial regeneration procedures. Such a temperature control system is described in U.S. Pat. No. 4,679,401, where a refrigerant gas is diverted and brought into heat exchange relationship with the first and/or second stage heat sinks of a cryopump. By controlling the flow and temperature of the diverted refrigerant gas the problems of crossover hangup and or achieving more efficient regeneration can be addressed.